DE2231939B2 - PROCESS FOR ELECTRICALLY NICKEL-PLATING OF SURFACES MADE OF METAL, PLASTIC AND CERAMICS - Google Patents

Description

35

The invention relates to a method for electroless nickel plating of surfaces made of metals, in particular non-ferrous metals and their alloys, metals of the iron group, aluminum and its alloys, plastic and ceramics, using a bath based on a solution of nickel salt, sodium citrate, ammonium chloride, ammonia and Sodium hypophosphite with a density of 1.075 to 1.091 g / cm ³ at 20 C.

There are baths known electroless nickel plating, substantially containing nickel salt, such as nickel chloride, nickel sulfate, reducing agents such as sodium For example, and complexing agents. Since nickel and reducing agent are constantly consumed during the nickel-plating process, in practice nickel is added to the baths in the form of nickel salt and reducing agent in order to maintain longer operation. However, it cannot be avoided that certain bath constituents, in particular the oxidation products of the reducing agent and the anion content of the nickel salt, accumulate in the electrolyte. As a result, the bath density increases constantly.

Furthermore, since the pH value of baths for electroless nickel-plating continuously falls during operation, the electrolyte is also mixed with alkali in the form of ammonia or sodium hydroxide. ^6s

Now the addition of nickel salt, reducing agent and alkali takes place at the working temperature of the Electrolytes (usually around 100 C), then at least partial spontaneous local reduction occurs with the formation of nickel nuclei, which disturb the further operation of the bath or make it impossible power. In addition, when alkali is added to correct the pH, a whitish cloudiness occurs as a result of precipitation of nickel hydroxide built into the nickel coating and its properties unfavorable influenced. The appearance is deteriorated and the corrosion resistance is lowered. the The surface has a roughness that is often disruptive.

In order to avoid the disadvantages described, use known methods of electroless nickel plating, z. B. the Kanigen method described in US Pat. No. 2,658,839, a circulatory system. The electrolyte is first cooled and after adding the supplementary solution in one for it provided reserve tank is heated up again and fed to the working bath. The implementation The facilities required for this process are complex, complicated and expensive.

Despite this effort, the baths operated in practice according to known methods must be in Consequence of the above-mentioned enrichment of certain bath components at certain time intervals as a whole be discarded.

According to Austrian patent specification 1 95 7i () nickel, hypophosphite and OH ions are added to baths for electroless nickel plating, whereby the The dependence of the concentration of these three components on each other leads to a control of the bath the change in pH is used.

From the American patent 28 37 445 a continuous process for electroless nickel plating is of metals known in which a bath containing nickel sulfate and sodium hypophosphite is used with lactic and propionic acid as a complexing agent and accelerator. Using a The addition of the supplementary solutions takes place in a separate container at a lower temperature. Not only nickel salt and hypophosphite are added during operation as well as a pH correction, but also lactic and propionic acid in one Amount that is in a certain constant ratio to the amount of nickel added. This will make the Phosphite tolerance of the bath increased. By increasing the concentration of phosphite and sulfate ions as well of complexing agents, the total salt concentration of the electrolyte increases continuously.

In order to avoid the disadvantage of constantly changing the bath composition, according to the in German Offenlegungsschrift 16 21344 described Apply a solution to the bath continuously or at regular intervals Nickel salt, complex salt and ammonia and separately mixed with a sodium hypophosphite solution, Periodically a certain volume fraction of the electrolyte is taken from the bath and this is replaced by water replaced so that the density of the bath is always below 12 Be.

In this way it is achieved that the composition of the bath is constant on average. As a result of these are nickel coatings with a significantly improved uniformity with regard to their properties obtain. By simultaneously adding nickel salt and complexing agents (sodium citrate) with the Supplementary solution, the tendency of the bath to decompose is also reduced.

3 4

NEN added at working temperature (about 100 C) is another significant advantage of the invention that will. The stability of this bath, however, satisfies the deposition rate in a certain way not quite yet. At densities above 12 Be at 20 C range a function that occurred in the unit of time Cloudiness due to the precipitation of whitish deposits of nickel and this is roughly proportional. propose nickel compounds that lead to a 5 The deposition rate of the bath according to Deterioration in the properties of the nickel over the invention is - depending on the amount of additional trains to lead. Local dissolutions also form - normally 5 to 10 μm, at most Settlement in overheated areas of the bath, e.g. B. at bath 15 μΐη / h. The bath temperature should be as high as possible warm or heated walls quickly nickel deposits, and is usually 98 to 100 C. In the case of which means frequent cleaning of bath tanks and heating nickel-plating of aluminum and some art facilities makes necessary. materials are used at a lower temperature (60 to 80 C)

The object of the invention is a continuous increase and higher pH value (7 to 8), but otherwise below

drive to electroless nickel plating without applying the same conditions. Another

a complex bath circuit with evaporation and the advantage of the process according to the invention is through

Filtration. i _{5 given the} following fact: in baths to the currentless

According to the invention, this object is achieved by nickel plating, the deposition rate is achieved in that the bath at a bath temperature of 60 to 100 C immediately at the beginning of the nickel plating is initially lower in short time intervals and then more or less such amounts of a concentrated supplementary solution increases quickly . When using baths with a higher concentration of nickel salt, sodium citrate, ammonium chloride and ao starting concentration, this increase is very rapid. Ammonia, in which nickel is a complex compound. If the supplementary solutions are added frequently, the maximum achievable phit supplementary solution is added to a concentrated sodium hypophosphate and the rate of deposition is achieved in a short time (approx. 0.5 h). Also the rela-bath periodically during operation such a moderately high pH value has an effect in the direction of a ge electrolyte solution removed and water as an increase in the deposition rate. is replaced, that the density of the bath between non-kept In the method of the current-1.091 to 1.161 g / cm ³ and the pH adjusted to 6 to 8 are nickel is in their properties. According to the method according to the invention, completely uniform, shiny, smooth, firmly adhering, corrosion-resistant nickel coatings are achieved by adding a concentrated supplementary solution, a nickel complex salt bath solution containing nickel, sodium citrate, ammonium chloride and ammonia, even in larger volumes with unlimited life and the hypophosphite solution in connection with a permanent and excellent stability and is suitable periodic exchange (discarding) with a part for production-like electroless nickel-plating believolume an average constant bath composition big shaped parts made of metals such. B. iron, is maintained and a constant pH value is guaranteed. 35 copper, brass, aluminum and plastic. Above all, the nickel content in the bath and ceramic remains. In particular, it can also be large-medium constant. The phosphite concentration does not properly reach flat components and profiled molded parts the critical limit from which precipitation is nickel-plated.

entry. It is suitable for the process according to the invention. The bath and process according to the invention

«A practically unlimited service life 4 ° can also be used for electroless nickel-plating of

ensures what is especially important for continuous small parts in a drum.

Borrowed nickel plating in a manufacturing plant of The invention is illustrated by the following examples

Advantage is. The addition of the supplementary solution can be explained.

take place at working temperatures of 98 to 100 C, _R. 11

without a decomposition of the bath or a 45 Example]

Insoluble compounds precipitate. Metal (except aluminum) or ceramic counter-

According to the invention, when nickel-plating metal stands, according to one in electroplating

Oils and alloys at pH 6 to 7, in some cases the usual pretreatment in a nickel bath as follows

especially when nickel-plating aluminum Composition electrolessly nickel-plated:

Some plastics worked at pH 7 to 8. 5 <> _{nickel, sulfate (NiSO. 7} H ₂ O) 35 g / l

A particular advantage of the tri-sodium citrate according to the invention

It is important to use a stable ammonium- CH Na O · 5 5 HO) 100 s / l

chloride-containing nickel complex salt solution as a supplement ammonium chloride (NH ₄ Cl) '.'. '.'. '. 50 g / l

solution by d, e the pH of the bath is Na.riumhypophosph.t

Adjusts to 6 to 7 (preferably 6.2 to 6.6), without 55 (NaH PO -HO) 10 g / l

that normally during operation a pH u _w ^{2 2 2} 6 2 to 6 6

Correction becomes necessary. Temperature W '.'. W .. '.'. '.'. '.'. '.'. '.'. '. 98 to 100 C.

... ^E ! ^{n we} " ^e jf ^advantages . ' ^st the extraordinary rod ..- deposition rate ... 5 to 10 μm / h

did the electrolyte according to the invention. This stable surface loading of the bath up to 4 dm ² / l

tat enables the supplementary solutions to be added at ⁰⁰

Working temperature and prevents over longer loading All I 5 min the bath per dm ² hinged

the formation of nickel deposits on the surface of the goods 4 cm ^{3 of} an ammoniacal

Vessel walls and heating devices. ammonium chloride-containing nickel complex salt solution

The amount of (supplementary solution A) and 2 cm ^{3 of} reducing solution added in a certain time

In the process according to the invention, nickel is added ^{in 6} 5 (supplementary solution B),

at the same time practically completely used up. Will the O'c supplementary solutions have the following compo-

The amount of additional solutions increases, then the amount increases:

also the rate of deposition. It represents a supplemental solution A: nickel complex salt solution

Nickel sulphate 190 g / l

(corresponding to 40 g / l Ni)

tri-sodium citrate-5,5-hydrate 75 g / l

Ammonium chloride 38 g / l

Concentrated ammonia (25%). 250 cm ³ /!

Concentration and addition of the supplementary solutions as in Example 1.

Instead of nickel sulfate, an equivalent amount of nickel chloride can also be used.

Example 3

Supplementary solution B: reducing solution sodium hypophosphite 396 g / l

In the given approaches for the bathroom and plastic and black articles. B. from acrylic-nickel complex salt solution can be used instead of nickel- »o nitrile-butadiene-styrene copolymers (ABS)

sulfate, with regard to the nickel content, is also a pretreatment that is common in electroplating

equivalent amount of nickel chloride (NiCl ₂ · 6 H ₂ O) loss occurs in a nickel bath with the following combination

be turned. Composition electroless nickel-plated:

Example 2

. '' 5 objects made of aluminum are after a m

Pre-treatment processes common in electroplating in a nickel bath with the following composition electroless nickel-plated:

Nickel sulfate (NiSO ₄ · 7 H ₂ O) 35 g / I * °

tri-sodium citrate

(C ₆ H ₅ Na ₃ O ₇ · 5.5 H ₂ O) 100 g / l

Ammonium chloride (NH ₄ Cl) 50 g / i

Sodium hypophosphite

(NaH ₂ PO ₂ · H ₂ O) 10 g / l »5

pH 7 to 8

Temperature 70 to 80 C

Deposition rate ... 5 to 10 μm / h Surface treatment of the bath .... up to 4 dm ² / '

Nickel sulfate (NiSO ₄ · 7 H ₂ O) 35 g / 1

tri-sodium citrate%

(C ₆ H ₅ Na ₃ O ₇ · 5.5 H ₂ O) 100 g / l

Ammonium chloride (NH ₄ Cl) 50 g / l

Sodium hypophosphite

(NaH ₂ PO ₂ · H ₂ O) 20 g / l

pH 7.5 to

Temperature 60 to

Deposition rate ... 5 μπι / h surface loading of the bath up to 4 dm ²

Concentration and addition of the supplementary solutions as in Example 1.

Instead of nickel sulfate, an equivalent amount of nickel chloride can also be used.

Claims (4)

Patent claims: 1. Process for electroless nickel plating of surfaces made of metals, in particular non-ferrous metals and their alloys, metals of the iron group, aluminum and its alloys, plastic and ceramics, using a bath based on a solution of nickel salt, sodium citrate, ammonium chloride, ammonia and xo sodium hypophosphite with a density of 1.075 to 1.091 g / cm ³ at 20 C, characterized in that the bath at a bath temperature of 60 to 100 C in short time intervals in succession such amounts of a concentrated supplementary solution of nickel salt, sodium citrate, ammonium chloride and ammonia, in the nickel is present as a complex compound and is added to a concentrated sodium hypophosphite supplement solution and such an amount of electrolyte solution is periodically removed from the bath during operation and replaced by water that the density of the bath is between 1.091 to 1.161 g / cm ³ and the pH is maintained at 6-8. 2. The method according to claim 1, characterized in that the supplementary solutions at a »5 Bath temperature of 98 to 100 C can be added. 3. The method according to claim 1, characterized in that at 60 to 80 C and a pH of 7 to 8 is nickel-plated. 4. The method according to claim I, characterized in that at 98 to 100 C and a pH of 6.2 to 6.6 is nickel-plated.